1. Field of the Invention
The present invention relates to a catalyst layer etc. used for a fuel cell membrane electrode assembly.
2. Background Art
Catalyst layers are used for conventional fuel cell membrane electrode assemblies.
A known catalytic electrode for a fuel cell includes a catalyst layer having aegagropila-linnaei-shaped carbons made by spherically growing a nanocarbon material with a diamond particle as a nucleus and causing the nanocarbon material thus grown to support a platinum group catalyst. Further, a known solid polymer electrolyte fuel cell electrode containing carbon particles which are monolayer carbon nano-horn aggregates in which monolayer carbon nano-horns made up of monolayer carbon nano-tubes of a unique structure having a conical shape at one end are aggregated into balls.
FIG. 18 is a drawing showing a structure of a conventional catalyst layer. The conventional catalyst layer is homogeneously filled with support materials.
However, catalyst layers used for conventional fuel cell membrane electrodes suffer the following problems.
Since a catalyst layer is homogeneously filled with support materials, densely filling the catalyst layer with the support materials so as to make the catalyst layer compact will make pore size and porosity small, resulting in a lower material diffusibility. Extracting a high current using the catalyst layer with a lower material diffusibility will lead to insufficient release of generated gas from an anode and insufficient discharge of generated water from a cathode and to insufficient feeding of fuel and air. This is likely to drop power generation performance of a fuel cell. Although the compact (i.e. thin) catalyst layer has advantage in terms of proton conduction in the catalyst layer, since the length of proton diffusion is short, it is difficult to keep pore size and porosity large, when the catalyst layer is compact.
Since the catalyst layer has nonconductive diamond particles in aegagropila-linnaei-shaped carbons, a fuel cell catalyst electrode suffers low electronic conductivity, resulting in lower power generation performance of a fuel cell.
A carbon nano-horn in a carbon nano-horn aggregate and the central nucleus of the carbon nano-horn aggregate contact with each other only at one point. Consequently, it is highly likely that contact between carbon nano-horns get broken. This is highly likely to result in drop of electronic conductivity (power generation performance). Further, such structure is unstable as a structure of a catalyst layer.
The present invention was made in view of the foregoing problems. An object of the present invention is to provide a catalyst layer, a fuel cell membrane electrode assembly, and a fuel cell, each of which has a compact size and has excellent power generation performance, and a method for producing the catalyst layer, the fuel cell membrane electrode assembly, and the fuel cell.